The lawyer in me is compelled to give a disclaimer: I am not an electrician nor do I play one on sewing machine forums; this post should not be considered electrical advice; for electrical advice you should consult a qualified electrician in your area.
The 66 had no plug on the machine, all the wire connections were in a housing under the motor. I could adapt this to a machine with a plug on the machine itself, I just haven't. My wiring is diagrammed in the picture (not sure if my electrical symbols are correct).